Electromagnetic actuating device



April 2, 1968 J. c. MACY 3,376,528

LECTROMAGNETI C ACTUATING DEVI CE Filed Sept. 10, 1965 '7 Sheets-Sheet 1FlG.l

INVENTOR. JAMES C. MAC) A. TTORNEYS.

April 1968 J. Q. Ma 3,376,528

ELECTROMAGNETIC ACTUATING DEVICE Filed Sept. 10, 1965 '7 Sheets-Sheet 2INVENTOR. JAMES C. MACY 4 T TORNEYS.

April 2, 1968 J. c.- MACY 3,376,528

ELECTROMAGNETI C ACTUATING DEVI CE Filed Sept. 10, 1965 7 Sheets-Sheet 3F I63 A F'IGISB INVENTOR. JAMES c. MA c") V ATTORNEYS.

April 68 J. c. MACYV 3,376,528

ELECTROMAGNETIC ACTUATING DEVICE Filed Sept. 10, 1965 7 Sheets-Sheet 1INVENTOR. JAMES C. MA Y A T TORNE Y5.

April 2, 1968 J. c. MACY 3,376,528

ELECTROMAGNETIC ACTUATING DEVICE Filed Sept. 10, 1965 '7 Sheets-Sheet 5INVENTOR. JAMES C. MAC Y A TTORNEYS.

FIGS

J. C. MACY ELECTROMAGNETIC ACTUATING DEVICE April 2, 1968 7 Sheets-Sheet6 Filed Sept. '10, 1965 INVENTOR. JAMES c. MACY W k M Z Arm/ 55% A ril2, 1968 J. c. MACY '7 Sheets-Sheet 7 Filed Sept. 10, 1965 w wmmwWMwW amhvvnv Q .FIC3.7'

INVENTOR. JAMES c. acy

3,376,528 ELECTROMAGNETIC ACTUATING DEVICE James C. Macy, Westfield,N..l., assignor, by mesne assignments, to Thrust, Incorporated, NewYork, N.Y., a

corporation of New Jersey Filed Sept. 10, 1965, Ser. No. 486,454 22Claims. (Cl. 335-296) ABSTRACT OF THE DISCLOSURE This invention relatesto electromagnetic actuating devices, and more particularly, to a noveltype of electromagnetic actuating device capable of providing a powerfulmechanical force over a relatively long traverse. This novelelectromagnetic device is referred to as a contractuator.

The conventional electromagnetic relay includes an electrical coil, amovable magnetic armature, and a magnetic structure for completing theflux path around the coil. Devices of this general structure can providea relatively powerful mechanical force as the armature is attracted inrespouse to energization of the coil. However, the magnitude of theforce is inversely proportional to the square of the working air gaplength associated with the armature. Thus, any attempt at increasing thelength of the stroke brings about a decrease in the force at thebeginning of the stroke which is approximately proportional to thesquare of the distance to be traversed. Electrical devices of thisgeneral structure are, therefore, inherently short stroke devices.

By comparison, the conventional plunger-type solenoid is inherently along stroke device and usually includes an iron plunger adapted to passthrough the center of an electromagnetic coil. The mechanical force iscreated by the interaction between the magnetic flux of the plunger andthe current passing through the energizing coil. The force created bythe solenoid is relatively weak and suffers from the furtherdisadvantage of being strongest at the middle of the stroke and weakestat the ends where maximum force is often required.

Electromagnetic devices can be classified either with the inherentlyshort powerful stroke devices, or with the relatively long weak strokedevices. Because of the inherent characteristics of the priorelectromagnetic devices it has not been possible to achieve a powerfulforce over a relatively long traverse without resorting to variousboosting or supplementing techniques.

An object of this invention is to provide an electromagnetic actuatorcapable of converting electrical energy into a relatively powerful forceover a long traverse.

Another object of the invention is to provide an electromagneticactuator which can achieve optimum performance for given size, weight,geometrical configuration and electrical power conditions.

Another object is to provide an electromagnetic actuator in which thecreated force can be controlled as desired throughout the stroke.

Still another object is to provide an electromagnetic actuator which canbe readily mass produced and in which standardized components can beassembled to satisfy varying operational requirements.

ire States Patent Yet another object is to provide an electromagneticdevice which can easily be integrated as an operational portion of asystem.

The electromagnetic device constructed in accordance with this inventionconverts electrical energy directly into mechanical force and is capableof providing a powerful mechanical force without limitation on thelength of the stroke or traverse. The force is created by the magneticattraction exerted upon a plurality of interconnected magnetic members.The working gap is broken into small increments so that a substantialforce can be created without suffering the normal effects associatedwith a long stroke.

The invention is described in greater detail with reference to thefollowing specification which sets forth several illustrativeembodiments. The drawings are part of the specification wherein:

FIGURE 1 is a view of the actuating device in accordance with oneembodiment of the invention with portions broken away for clarity ofillustration;

FIGURE 2 is an exploded perspective assembly drawing showing details ofsome of the components for the actuating device in FIGURE 1;

FIGURES 3A and 3B are schematic diagrams illustrating two arrangementsfor interconnection of the electromagnetic coils for the unit in FIGURE1.

FIGURE 4 is a partial cross sectional view illustrating anotherembodiment of the invention;

FIGURE 5 is a cross-sectional view of another actuating device inaccordance with this invention wherein a single energizing coil isemployed;

FIGURE 6 is a view of a helical actuating device in accordance with thisinvention with portions broken away for clarity of illustration;

FIGURE 7 similarly illustrates another helical actuating device; and

FIGURE 8 is a cross-sectional View showing the structure of the helix inFIGURE 7.

The mechanical force created by an electromechanical device can beexpressed by the following formula:

where P is the pull or force, k is a constant, F is the magnetomotiveforce, a is the permeability of the working gap, A is the area of thepole face, and x is the length of the working gap. It should be notedthat the created force is inversely proportional to the length of theworking gap. In addition, the magnetomotive force is inversely relatedto the gap length and therefore the force falls ofl rapidly as theworking gap length increases.

In the illustrative embodiments, structures are described which providea powerful force over a relatively long traverse which would normallyrequire a corresponding long air gap. With the structure in accordancewith the invention, the air gap is broken into relatively smallincrements to eliminate the problems associated with the long air gap.The structurealso makes possible a relatively high magnetomotive forceby minimizing the flux losses and by permitting use of materials in theworking gap having a permeability greater than air.

The actuating device in accordance with one embodiment of the inventionis illustrated in FIGURES 1 and 2, and includes a plurality ofdisc-shaped members 10, for convenience referred to as coil discs, eachincluding an inner ring 11 and an outer ring 12. A concentrically woundelectrical coil 14 is located between the inner and outer rings of thedisc which form core pieces for the coil. A shoulder is machined in theupper and lower edges of rings 11 and 12 for positioning a pair ofnonmagnetic washers 15 above and below coil 14. Coil 14 can therefore becompletely enclosed to avoid exposure to the surrounding fluid.

Inner core piece 11 includes a groove 16 extending from its innersurface to thereby provide an upper annular flange 17 and a lowerannular flange 18. An associated coupling disc 20 is externally machinedabout its periphery to cooperate with the groove and flanges on "theinner surface of core piece 11. The thickness of the coupling disc isthe same as the thickness of coil disc 10. A circumferential groove 21is machined surrounding disc 20 to provide upper and lower peripheralflanges 22 and 23. The coupling discs 20 are loosely mounted on a guideshaft 26 passing through the center thereof with a coupling disc locatedbetween each adjacent pair of coil discs. The flanges on the inner corepieces of adjacent coil discs rest within the groove 21 of theassociated coupling disc and the flanges of adjacent coupling discs restwithin the groove 16 of the associated inner core piece. Thisinterlocked groove and flange arrangement permits the coil discs to movetogether until they touch one another, or to separate until the flangesengage. Thus, the coupling discs limit the separation between coil discsand, hence, determine the maximum working gap which can exist betweenadjacent coils and core pieces. Guide shaft 26 maintains the coil discsin alignment parallel to one another and insures that the movement ofthe coil discs in linear and parallel to the axis of the shaft.

The end cap 30 is preferably machined from a single piece of iron andincludes an annular recess dimensioned to accommodate acircumferentially wound electrical coil 31 and a nonmagnetic washer 32.A coupling member 34 is pivotably mounted in the center of end cap 30 ina manner which prevents any longitudinal movement relative to the 'endcap. The coupling member is constructed so that the portion extendedabove the end cap (as viewed in FIGURE 2) is essentially the same as theportion of a. coupling disc extending from one of the coil discs. Morespecifically, coupling member 34 includes a peripheral flange 35 adaptedto rest within the groove 16 of the adjacent coil disc, and a groove 36adapted to cooperate with the flange of the adjacent coil disc- Theother end of the coupling member is shaped as required for attachment toexternal equipment.

The upper and lower end caps for the actuating device are essentiallythe same and are attached to the upper and lower coil discs in the samefashion as is illustrated in FIGURE 1. The coupling members 34 eachinclude a central recess 37 therein adapted to loosely hold guide rod26. The length of the guide rod and the length of the cooperatingrecesses are selected so that the rod cannot fall out when the actuatingdevice is in the fully extended condition but at the same time permitthe actuating device to contract until the coil discs touch one another.

Although the flanges 22 and 23 on the coupling disc, and flanges 17 and18 in the coil disc, are shown as complete circumferential flanges theycould be formed as flange segments covering somewhat less than half ofthe circumference. Such an arrangement would have assembly advantagessince the coupling disc could then be inserted within a coil disc andthereafter turned so that the flange segments become juxtaposed.

A flexible bellows-like cover structure 40 is mounted surrounding theunit to form a dust cover and thereby keep dirt and dust out of the airgaps between the coil discs or, if a fluid other than air is placedbetween the discs, cover 40 prevents this fluid from escaping. The outerrings of the coil discs are provided with grooves 41. Retaining rings 42surround the bellows cover structure and cooperate with grooves 41 tomaintain the cover in its proper position.

Retaining rings 42, coupling discs 20, coupling members 34 and guide rod26 are preferably constructed from nonmagnetic materials such asaluminum or brass. The inner and outer core pieces 11 and 12, and theend caps 30, are constructed from a magnetic material such as iron andcan be laminated if desired to reduce eddy current losses.

The electrical leads from the coils 14 and 31 can be brought out throughsuitable holes in the outer core pieces and end caps. If the coils areinterconnected so that current flows through each coil in the samedirection, for example, the clockwise direction as shown in FIGURE 3A,the coil discs will be attracted to one another and an overallcontracting force is provided as indicated by the arrows. On the otherhand, if the coils are interconnected in an alternate fashion as shownin FIG- URE 3B where current passes through one coil in a clockwisedirection and through adjacent coils in a counterclockwise direction,the coil discs tend to repel one another and an overall expanding forceis provided as indicated by the arrows. With suitable externalswitching, the same unit can be used to provide either a contracting orexpanding force. The electrical coils can be energized simultaneously orsequentially depending on the type of motion desired.

The maximum linear traverse of the actuating unit, that is, the maximumdistance that one end coupling member moves relative to the other whenthe coils are energized, is equal to the sum of the incremental workinggaps 45 existing in the fully extended condition. If it is desired toincrease the travel distance, this is easily accomplished by addingadditional coil discs and coupling discs intermediate end caps 30.Therefore, the travel distance can be increased without decreasing thecreated force since the force is a function of the working magnetic gapassociated with the individual coils. This working gap in turn islimited by the coupling discs so that a working magnetic contact ismaintained between the core pieces of adjacent coil discs.

Another embodiment of the invention is illustrated in FIGURE 4 whereinthe inner rings or inner core pieces 11' of the coil discs are looselymounted directly upon guide rod 26. The maximum gap 47 beween adjacentcoil discs is limited by inwardly flanged nonmagnetic coupling rings 46which surround the adjacent flanges 48 of the adjacent coil discs. Thecoupling rings thus replace the coupling discs as well as thesurrounding dust cover shown in FIGURE 1.

Another embodiment of the invention, utilizing a single electric coil,is shown in FIGURE 5. The coil 50 is a cylindrical, concentricallywound, coil encased in a suitable nonmagnetic material providingrelatively smooth exterior surfaces. One end of coil 50 is accommodatedwithin a suitably dimensioned resistively coated annular recess 51 in anend cap 52. In recess 51, between the end coil 50 and the bottom of therecess, is a flat coil spring 53 constructed from an electricallyconductive material. The coil spring maintain electrical contact betweenan external lead 54 and one of the electrical leads 55 emerging fromcoil 50. The other end of coil 50 is similarly accommodated in anannular recess 61 within an end cap 62. The other lead 65 of coil 50 iscoupled to an external lead 64 via a coil spring 63 located withinrecess 61. End caps 52 and 62 include extensions 57 and 67,respectively, adapted for attachment to external equipment.

Within the central opening of coil 50 there are a plurality ofinternally grooved and flanged discs 76 which are coupled to one anotherand to the end caps by means of externally grooved and flanged couplingdiscs 77. The coupling discs serve to limit the length of the workinggap in essentially the same manner as previously described with respectto FIGURES 1 and 2. A plurality of externally flanged and grooved discs78 surround coil 50 and are coupled to one another and to the end capsby means of internally flanged coupling rings 79. The coupling ringsoperate to limit the length of the air gap between discs 78 inessentially the same manner as previously described with respect toFIGURE 4.

End caps 52 and 62, and discs 76 and 78, are preferably constructed froma magnetic material such as iron whereas coupling discs 77 and couplingrings 79 are constructed from a nonmagnetic material.

When coil 50 is energized, a magnetic flux is created which passesthrough discs 76 and 78 and end caps 52 and 62 creating a force tendingto pull the end caps together to thereby eliminate the working magneticgaps 80 existing between the discs.

In the previously described embodiments of the invention the magneticcore structure has included individual segments disposed to break theworking magnetic gap into smaller increments. In the embodiment of theinvention shown in FIGURE 6 the segments of the magnetic structure arepart of the same helical core structure. More specifically, the unit inFIGURE 6 includes a helical conductor 90 surrounded by electricinsulation 91. Conductor 90 may be a single copper bar, or may bestranded including a plurality of separate conductors. The ends ofconductor 90 are attached to suitable leads 89 brought out through theassociated end caps 92 and 93, the leads being connectable to a suitablesource of electric power.

The magnetic core structure associated with the helical conductorincludes an inner helix 94 and an outer helix 95, which are bothconcentric with respect to the helix of conductor 90. The ends of thecore helices are securely fastened to end caps 92 and 93 as by welding.

A cylindrical guide rod 98 passes through the center of inner core helix94. The ends of the guide rod are flanged outwardly and these flangesare accommodated within a suitable recess 100 within end caps 92 and 93.The recess includes a shoulder 99 adapted to cooperate wth the flange101 on the end of the guide rod. The cooperation between the flanges atthe end of the guide rod and the shoulders of the end caps serve tolimit the maximum distance between the end caps, and hence, the axiallength of the working gap between adjacent core segments. Furthermore,the guide rod maintains the structure in linear alignment. In some casesthe helical structure between the end caps will be relatively rigid andtherefore the guide rod can be eliminated. However, in most cases thestructure will be designed for maximum flexibility. For example, thecores 94 and 95 may consist of iron particles in a flexible medium andthe conductor 90 may consist of a multiple structure of relatively fineWires.

,When current passes through conductor 90, magnetic flux is createdsurrounding the conductor and in turn creates magnetic poles along theradial surfaces of the associated core helices. For example, the rightside of the outer core helix 95 a viewed in FIGURE 6 may become acontinuous helical north pole while the left side becomes a continuoushelical south pole. Under these circumstances, the right side of theinner helix would become a south pole and the left side would become anorth pole. It should be noted that the adjacent surfaces (oppositesides of the working gap) of a core helix are of opposite magneticpolarity and therefore tend to attract one another. As a result, endcaps 92 and 93 are drawn toward one another and the gap between adjacentsegments of the helices are eliminated.

Another helical embodiment of the invention is shown in FIGURES 7 and 8including two separate helices displaced by l80 from one another andeach disposed between the end caps. With two separate helices it ispossible to create contracting or expanding forces as desired. Each ofthe helices 114) and 111 includes a flat conductive strip 112 in thecenter sandwiched between a pair of flat strips 113 and 114 ofelectrically insulating material as can best be seen in thecross-sectional view in FIG- UR'E 8. The insulating strips are widerthan the conductive strip and secure a pair of magnetic strips 115 and116 in positions located radially inside and outside, respectively, ofthe conductive strip. The helical structure is completed by a pair ofstrips 117 and 118 wrapped around the outer edges of strips 115 and 116respectively. Strips and 117 form the inner core helix and strips 116and 118 form the outer core helix. The individual strips can be madefrom layers of metal foil, and hence, the entire structure can berelatively flexible. Also, it should be noted that the structure shownin FIGURES 7 and 8 can be produced continuously from. an automaticmachine and cut to length as required.

Two such helical structures 110 and 111 are secured between the end caps120 and 121. The helical structures are identical but displaced from oneanother so the segments of one helix nest between the segments of theother helix. The conductors, at the ends of the helical structure, areattached to leads 122 brought out through the end caps. The helicalstructures are physically secured to the end caps by any suitabletechnique such as weldmg.

If the conductors are so energized via leads 122 that current flowsthrough both helical structures in the same direction, e.g., clockwise,then a contracting force is created drawing the end caps together.However, if current flows through the helices in opposite directions,e.g., clockwise in one and counterclockwise in the other, then anexpanding force is created pushing the end caps apart.

FIGURE 8 shows the cross section of one helical structure 111, andsimilar adjacent cross section of the other helix 110. With current flowthrough the helical structures in opposite directions, the magnetic fluxwill be as shown in dotted lines and the magnetic poles created on thefaces of the magnetic core pieces will be as indicated by the lettersNaud S. In each case the opposite magnetic poles appear on opposingfaces and therefore they tend to repel one another. As a result, anexpanding force is created as indicated by the arrows.

In some installations operation can be optimized by further reducing thereluctance of the magnetic path. Accordingly, a fluid or elasticmaterial having ferromagnetic properties could be used to till theworking gap such as shown in FIGURE 4 where a fluid with ferromagneticproperties fills the gaps 47. This would have the eflect of decreasingthe magnetic flux losses in addition to decreasing the reluctance of themagentic path.

While only a few illustrative embodiments of the invention have beendescribed in detail it should be obvious that there are numerousarrangements and variations within the scope of this invention. Theinvention is more clearly defined in the appended claims.

What is claimed is:

1. In a magnetic actuating device, the combination of a pair of magneticend members capable of linear movelment along a common axis;

a magnetic structure disposed between said end members and including aplurality of magnetic segments surrounding said common axis for dividingany existing gap between said end members into a plurality ofapproximately equal increments; and

electromagnetic means operatively associated with said magneticstructure for creating a magnetic flux when energized, which magneticflux passes through said magnetic segments to cause relative movement ofsaid end members along said common axis.

2. A magnetic actuating device in accordance with claim 1 wherein saidelectromagnetic means comprises a plurality of electrical coils eachsurrounding said common axis and lying in a plane perpendicular to saidcommon axis; andsaid magnetic segments are core pieces each attached toand concentric with a diiferent one of said electrical coils.

3. A magnetic actuating device in accordance with claim 2 wherein a pairof core pieces are associated with each of said electrical coils, one ofsaid associated core pieces being disposed inside said coil and theother being disposed outside said coil.

4. A magnetic actuating device in accordance with claim 1 wherein saidelectromagnetic means comprises a single cylindrical electrical coilsurrounding said common axis and disposed between said end members, and

said magnetic segments are discs lying in planes perpendicular to saidcommon axis. 5. A magnetic actuating device in accordance with claim 4wherein some of said discs are disposed within said electrical coil andsome are disposed surrounding said coil.

6. A magnetic actuating device in accordance with claim 1 wherein saidelectromagnetic means is an electrical coil in the form of a helixsurrounding said common axis and said plurality of magnetic segments arepart of a helical core piece disposed concentrically of said electricalcoil.

7. A magnetic actuating device in accordance with claim 6 wherein saidmagnetic structure includes a pair of helical core pieces concentric tosaid electrical coil, one of said core pieces being located inside saidcoil and the other being located outside said coil.

8. In a magnetic actuating device, the combination of a magneticstructure including a plurality of relatively movable magnetic segmentsdisposed to provide a plurality of gaps between adjacent magneticsegments; guide means coupled to said magnetic segments for maintainingthe same in alignment and for restricting the movement thereof to adesired path;

movement limiting means coupled between said magnetic segments to limitsaid gaps therebetween and thereby maintain a working magnetic contactbetween said magnetic segments;

electromagnetic coil means operatively associated with said magneticsegments for creating a magnetic flux when energized, which magneticflux passes through said magnetic segments and said gaps therebetween tocause relative movement of said magnetic segments; and

a plurality of discs having a common axis and wherein saidelectromagnetic coil means comprises a plurality of separate coils eachsurrounding said common axis and each located in a separate one of saiddiscs, and

said magnetic structure comprises magnetic segments in the form of apair of concentric core pieces in each of said discs, the inner one ofsaid core pieces lying inside said coil and the outer of said corepieces lying outside said coil.

9. A magnetic actuating device in accordance with claim 8 wherein saidguide means comprises a cylindrical rod passing through the center ofsaid discs.

10. A magnetic actuating device in accordance with claim 8 wherein saidmovement limiting means comprises a plurality of externally flangedcoupling discs, and

said inner core pieces are flanged about a central opening and adaptedfor cooperation with said flanged coupling discs.

11. A magnetic actuating claim 8 wherein said movement limiting meanscomprises a internally flanged coupling rings and said outer core piecesare externally flanged and adapted to cooperate with the flanges of saidcoupling ring.

12. In a magnetic actuating device, the combination of a magneticstructure including a plurality of relatively movable magnetic segmentsdisposed to provide a plurality of gaps between adjacent magneticsegments;

guide means coupled to said magnetic segments for maintaining the samein alignment and for restricting the movement thereof to a desired path;

device in accordance with plurality of movement limiting means coupledbetween said magnetic segments to limit said gaps therebetween andthereby maintain a working magnetic contact between said magneticsegments;

electromagnetic coil means operatively associated with said magneticsegments for creating a magnetic flux when energized, which magneticflux passes through said magnetic segments and said gaps therebetween tocause relative movement of said magnetic segments; and wherein saidelectromagnetic coil means is a cylindrical coil having a central axis;and

said magnetic structure comprises a plurality of discs lying in parallelplanes and movable along said axis, said discs being disposed bothinside and outside said coil.

13. A magnetic actuating device in accordance with claim 12 whereinthose of said discs within said cylindrical coil are flanged about acentral opening and said movement limiting means comprises externallyflanged coupling discs adapted to cooperate with the flanges of saiddiscs.

14. A magnetic actuating claim 12 wherein those of said discs outsidesaid coil are externally flanged, and

said movement limiting means comprises internally flanged coupling ringsadapted to cooperate with said external flanges.

15. In a magnetic actuating device, the combination of a magneticstructure including a plurality of relatively movable magnetic segmentsdisposed to provide a plurality of gaps between adjacent magneticsegments; guide means coupled to said magnetic segments for maintainingthe same in alignment and for restricting the movement thereof to adesired path;

movement limiting means coupled between said magnetic segments to limitsaid gaps therebetween and thereby maintain a working magnetic contactbetween said magnetic segments;

electromagnetic co-il means operatively associated with said magneticsegments for creating a magnetic flux when energized, which magneticflux passes through said magnetic segments and said gaps therebetween tocause relative movement of said magnetic segments; and wherein saidelectromagnetic coil means is in helix and said magnetic structure is inthe form of a pair of concentric helices lying inside and outside thehelix of said coil.

16. A magnetic actuating device in accordance with claim 15 furthercomprising. a pair of end members coupled to the ends of said helicesand wherein said guide means and said movement limiting means comprise acylindrical member passing through the common center of said helices andcoupled to said end members to limit expansion of said helices.

17. In a magnetic actuating device, the combination of a plurality ofelectromagnetic coils each having a common axis;

a magnetic core member attached to and concentric with each of saidcoils;

guide means for maintaining said coils and concentric cores in parallelplanes with a plurality of gaps therebetween and for permitting movementalong said common axis;

separation limiting means coupled between said cores to limit the gapstherebetween; and

said electromagnetic coils when energized being operative to create amagnetic flux which passes through at least some of said core membersand gaps to cause relative movement of said core pieces.

device in accordance with the form of a 18. Apparatus in accordance withclaim 17 wherein each concentric core comprises a pair of core piecesand wherein the associated coil is between said core pieces.

19. Apparatus in accordance with claim 18 wherein the core piecesassociated with the intermediate coils are separated and wherein thecore pieces associated with the outermost of said coils are part of anintegral magnetic structure.

20. In a magnetic actuating device, the combination of a cylindricalelectromagnetic coil;

a pair of magnetic end members disposed at opposite ends of said coil;

a plurality of magnetic discs each disposed within said coil and flangedabout a central opening;

a plurality of nonmagnetic externally flanged coupling discs coupledbetween said inside magnetic discs and said magnetic end members tolimit the gap therebetween;

a plurality of externally flanged magnetic discs disposed outside saidcoil; and

a plurality of internally flanged nonmagnetic coupling rings coupledbetween said outside magnetic discs and said magnetic members to limitthe gap therebetween.

21. In a magnetic actuating device, the combination an electromagneticcoil means in the form of a helix having a central axis;

a pair of magnetic end members disposed at the ends of said coil andadapted for movement along said axis;

an inner helical core piece disposed within said helical coil andattached to said end members; and

an outer helical core piece disposed surrounding said helical coil andattached to said end members.

22. In a magnetic actuating device, the combination of a pair of endmembers;

a pair of similar helical structures each secured between said endmembers, each of said helical structures including a central helicalconductor and a pair of magnetic helical core pieces secured inside andoutside, respectively, of said conductor.

References Cited UNITED STATES PATENTS 25 BERNARD A. GILHEANY, PrimaryExaminer.

GEORGE HARRIS, Examiner.

